Why Does My Compost Smell? (And How To Control Odor)

  • By: composthq
  • Date: March 26, 2022
  • Time to read: 7 min.

Compost bins – contrary to the beliefs of some – should not smell bad. They should smell faintly of earth, and occasionally have a slightly sweet, rotten scent as food breaks down, but nothing strong or unpleasant.

You shouldn’t be able to smell your compost bin from a distance.

There are a number of different things that could make a compost bin smell unpleasant, and compost that smells bad usually has something going wrong with it – meaning that if you notice an unpleasant scent from your compost, it’s a good idea to look into it and address any issues.

So, let’s find out why does my compost smell? (And how to control odor).

My Compost Smells Like Sewage

If you notice a smell a little like toilets and drainpipes when you’re near your compost bin, the chances are that you have ended up with too much nitrogen in the heap.

Nitrogen comes from many “green” things you might add, such as grass clippings, green leaves, food waste, etc.

Note that green doesn’t refer to color, but to the fact that composts should be a mix of “green” and “brown” ingredients.

You can easily research what counts as a green ingredient, but anything that will break down fast and contains lots of moisture tends to be considered “green.”

Too much nitrogen can also cause an ammonia scent that is quite distinctive and strong. You will want to address this issue and restore balance to your compost heap so that it doesn’t stink up the garden.

What Should I Do?

You’re going to want to add “browns” to balance out the nitrogen. Shredded newspaper or cardboard are good options.

Twigs, sawdust, straw, nutshells, etc., all count as “browns.” They are high in carbon and tend not to have much moisture in them. They are also slower to rot.

Add plenty of “browns” and turn your compost heap if you can to disperse your browns throughout it, mixing them with the nitrogen-rich greens and breaking them up.

Sometimes, a compost heap with lots of nitrogen can be heavy and difficult to deal with.

If you find the heap too hard to turn, create some “pockets” in it using your trowel and add the browns to these.

They will increase the airflow and as the heap starts to break down and re-balance, you should be able to turn it properly.

If you really want to get rid of the smell fast, you can spread out your compost on a sunny day. The sun will help the ammonia evaporate and reduce the smell.

It will also dry out some of the excess moisture. However, this is quite a lot of work and can be messy.

My Compost Smells Like Rotten Eggs

This is one of the least pleasant smells you can get from your compost. It is usually a result of there not being enough oxygen in the heap.

The compost can be broken down either by aerobic bacteria (that need oxygen) or anaerobic bacteria (that need an absence of oxygen).

If your heap gets very compressed, the aerobic bacteria will die off and the anaerobic ones will thrive. You don’t want this to happen.

When anaerobic bacteria take over, you get a byproduct of hydrogen sulfide, and this stinks

There can be a number of reasons for your heap getting too compressed and the bacteria running out of oxygen, so you’ll need to work out the cause before you can address it.

The first reason is that you’ve added too much nitrogen. The aerobic bacteria become very active when they have plenty of nitrogen, and their activity warms your compost heap up – which unfortunately makes it more compressed.

This then squashes out the oxygen, and causes the aerobic bacteria to die off.

Another possible cause is the compost heap getting too wet, or containing too many moist ingredients.

If the heap is waterlogged, no oxygen can get into it, and again, you’ll lose aerobic bacteria and get anaerobic bacteria.

You may also notice that the pile turns slimy and green. Waterlogging is a particular problem in spring.

Finally, it may just be that you don’t turn the heap often enough. Any compost heap can get squashed down and end up anaerobic if it doesn’t have a little bit of attention from time to time.

Try and turn your compost heap whenever you can; the more you do, the happier it will be.

What Should I Do?

There are a few solutions to this issue. If you have too much nitrogen, try to recreate a balance by adding more browns to the heap, as suggested above.

Next, turn your compost heap thoroughly. Even if you have a good level of greens and browns, you can end up with an imbalance if they aren’t mixed.

Turning the heap adds air to it, combating the problem at its source. Throw in some sticks and twigs to help create air pockets and keep oxygen circulating within the heap. This will also help with drainage.

If your compost heap is getting too wet on a regular basis, you may want to either alter your compost bin setup or change what you put into the compost.

If your bin is somewhere that gets rained on a lot, consider adding a lid, or a sloped board to help divert the flow of rainwater.

If you’re adding too much wet food, either try and drain off excess moisture, or increase the amount of cardboard and paper you add.

You can ask neighbors for some newspaper or shredded card if you don’t have enough. This will help absorb some of the liquid in the heap.

My Compost Smells Like Rotting Food

Composts may smell like rotting food from time to time, but if the smell is strong or persistent, check what you are putting into the compost.

Meat, fish, and dairy are not very good additions, because they tend to smell, and they can also take a long time to decompose.

The same goes for oil and fats. These don’t break down easily and can turn rancid and make the compost heap smell unpleasant.

What Should I Do?

Stop including them. Try to change your cooking habits so that you don’t have waste meat or dairy, and put what you do have into landfill if it’s causing problems with your composter.

Freeze scraps that might otherwise go to waste, and try to use them on another day.

Alternatively, look into other composting systems, such as Bokashi bins or hot composting. These may be able to better deal with these types of foods.

Tiny amounts of meat, dairy, fish, and fat won’t do any harm in a large, active compost heap, so don’t worry if little bits creep in, but you don’t want to be adding these things on a regular basis or in large quantities, or your compost heap could start to smell very unpleasant.

How Else Can I Reduce Odors?

If you’re still having issues with the smell of your compost bin, or if you want to know what further measures can be taken, you may want to consider a tumbling composter.

Most of the problems that cause a bad smell in compost are readily solved by turning the compost – but that can be hard, heavy work, especially if you have a large compost heap.

It also isn’t very pleasant if the heap has gone wrong and smells bad.

A tumbling composter is specifically designed to let you move and aerate the compost without having to break your back doing it. Regularly turning your compost will also make it decompose faster, so a tumbling composter will give you a more efficient system.

This is especially valuable if you have a lot of high-nitrogen ingredients to compost – such as lots of grass clippings.

These can easily overwhelm a normal compost bin, but if you put them in a tumbling one, they will be broken down very quickly by the nitrogen-loving aerobic bacteria, without causing compaction issues.

Another option is a hot composter. These break ingredients down fast because they operate at higher temperatures, so they can be a great choice if you want compost quickly.

They will also usually overcome issues with odor, although they can still go wrong, and you will need to turn them regularly.

Conclusion

If your compost bin smells bad, pay attention; it does mean that something is wrong. Check your balance of greens, and check your moisture levels.

If your compost is too wet, add cardboard to dry it out. If your compost is too rich in nitrogen, throw in dry leaves or straw or twigs.

Turning your compost regularly is the best way to keep it operating efficiently, make sure the ingredients are well-mixed, and avoid problems with compaction and anaerobic bacteria.

You can just use a garden fork to stir up, lift, and mix the bin, or you can buy a special compost bin that has been designed to aerate for you.

Many people are afraid they will go wrong with composting, or afraid all their neighbors will hate them if they try it.

Don’t be! Compost heaps can smell bad if you make a mistake, but it is easy to rectify even drastic mistakes, and you’ll soon have your compost back on track and smelling like nothing but soil.

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